A bit off your question but related, at our recent tractor show some of my buddys (I have at least 2 lol) were arguing over who "owned" a certain tractor because a friend parked one of their tractors on another friends space. I reiterated the old wives tale "Posession is 9/10 of the law" and explained to them as a "current peaceful posessor" that person (whose space tractor was parked in) has superior claim to all others EXCEPT the rightful owner. In other words, I have no legal right to that tractor over my buddy (whose space it was parked in) just because he (in this case posesses it) stole it from another person, i.e. I cant defend my taking of it in court by proclaiming "ITS NOT HIS HE STOLE IT" Again, he is the "current peaceful posessor" so his right is superior over mine even if he did steal it.
ALSO RELATED TO BILL OF SALE ISSUES Then theres the whole other "buyer in good faith for consideration" can of worms where if an item is stolen (seller stole it) but the buyer was not aware of that and pays good money for it, thats a good defense against such things as receiving stolen property etc BUT THE RIGHTFUL OWNER still deserves the property back. In that case the buyer has no cause of action against the true owner so he has to bring action against the thief for his money back.
A "Bill of Sale" is good evidence of rightful posession of personal property and good evidence you paid consideration, it doesnt necessarily address "good faith" however. The sales price, description of property, language of conveyance, and signature and date are pretty much the essentials.
Hey I dont practice personal property law (if Mike or Dean disagree, theyre probably right) so NO WARRANTY but this is how I understand it AND IM THE CURRENT PEACEFUL POSESSOR OF THAT KNOWLEDGE LOL